dmstats: only generate aux data separator if group tag is defined

Fix a bug in _stats_set_aux() that causes bogus data to appear
in the 'userdata' field of stats reports when previously grouped
regions are ungrouped:

/var/tmp/File With Spaces: Created new group with 1 region(s) as group ID 0.

Removed group ID 0 on fedora-root

Name             GrpID RgID ObjType RgStart RgSize  #Areas ArSize  ProgID  UserData
fedora-root          -    0 region    6.39g 100.00m      1 100.00m dmstats #-
                                                                           ^^
This is the aux_data separator character followed by empty user data.
The _stats_set_aux() function should only emit the separator if
there is a valid group descriptor for the region.

libdm/libdm-stats.c

@@ -1954,10 +1954,9 @@ bad:
 static int _stats_set_aux(struct dm_stats *dms,
 			  uint64_t region_id, const char *user_data)
 {
-	const char *group_tag = NULL;
+	char *group_tag = NULL, *group_tag_escaped = NULL;
 	struct dm_task *dmt = NULL;
 	char msg[STATS_MSG_BUF_LEN];
-	char *group_tag_escaped = NULL;
 
 	/* group data required? */
 	if (_stats_group_id_present(dms, region_id)) {
@@ -1970,8 +1969,7 @@ static int _stats_set_aux(struct dm_stats *dms,
 		group_tag_escaped = _stats_escape_aux_data(group_tag);
 		if (!group_tag_escaped)
 			goto bad;
-	} else
+	}
-		group_tag_escaped = dm_strdup("");
 
 	if (dm_snprintf(msg, sizeof(msg), "@stats_set_aux " FMTu64 " %s%s%s ",
 			region_id, (group_tag_escaped) ? group_tag_escaped : "",
@@ -1984,7 +1982,7 @@ static int _stats_set_aux(struct dm_stats *dms,
 	if (!(dmt = _stats_send_message(dms, msg)))
 		goto_bad;
 
-	dm_free((char *) group_tag);
+	dm_free(group_tag);
 	dm_free(group_tag_escaped);
 
 	/* no response to a @stats_set_aux message */

test/shell/dmstats-group-ungroup-nouserdata.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+# Copyright (C) 2023 Red Hat, Inc. All rights reserved.
+#
+# This copyrighted material is made available to anyone wishing to use,
+# modify, copy, or redistribute it subject to the terms and conditions
+# of the GNU General Public License v.2.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+SKIP_WITH_LVMPOLLD=1
+SKIP_WITH_LVMLOCKD=1
+
+. lib/inittest
+
+# Don't attempt to test stats with driver < 4.33.00
+aux driver_at_least 4 33 || skip
+
+# ensure we can create devices (uses dmsetup, etc)
+aux prepare_devs 1
+
+GROUP_NAME="group0"
+BAD_USERDATA="#-"
+
+# Create a region and make it part of a group with an alias
+dmstats create "$dev1"
+dmstats group --alias "$GROUP_NAME" --regions 0 "$dev1"
+dmstats list -ostats_name |& tee out
+grep "$GROUP_NAME" out
+
+# Ungroup the regions then remove them
+dmstats ungroup --groupid 0 "$dev1"
+
+# Verify userdata does not contain '#-'
+dmstats list -ouserdata |& tee out
+not grep "$BAD_USERDATA" out
+
+# Clean up
+dmstats delete --allregions "$dev1"

test/shell/dmstats-group-ungroup-userdata.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+
+# Copyright (C) 2023 Red Hat, Inc. All rights reserved.
+#
+# This copyrighted material is made available to anyone wishing to use,
+# modify, copy, or redistribute it subject to the terms and conditions
+# of the GNU General Public License v.2.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+SKIP_WITH_LVMPOLLD=1
+SKIP_WITH_LVMLOCKD=1
+
+. lib/inittest
+
+# Don't attempt to test stats with driver < 4.33.00
+aux driver_at_least 4 33 || skip
+
+# ensure we can create devices (uses dmsetup, etc)
+aux prepare_devs 1
+
+GROUP_NAME="group0"
+USERDATA="foo"
+
+# Create a region and make it part of a group with an alias
+dmstats create "$dev1" --userdata "$USERDATA"
+dmstats group --alias "$GROUP_NAME" --regions 0 "$dev1"
+dmstats list -ostats_name |& tee out
+grep "$GROUP_NAME" out
+dmstats list -ouserdata |& tee out
+grep "$USERDATA" out
+
+# Ungroup the regions then remove them
+dmstats ungroup --groupid 0 "$dev1"
+
+# Verify userdata is still valid
+dmstats list -ouserdata |& tee out
+grep "$USERDATA" out
+
+# Clean up
+dmstats delete --allregions "$dev1"